The haze or smog was so serious that the winter running _________.Some students complained as they ran
| A．could have cancelled | B．should have cancelled |
| C．must have been cancelled | D．ought to have been cancelled |
No one is allowed ______ in the classroom.
| A．smoking | B．smoke | C．smoked | D．to smoke |
The rice made _____ possible to produce one-third more of the crop in the same field.
| A．that | B．this | C．one | D．it |
I regret ______ you that you will miss your flight if you don’t hurry up. You have only twenty minutes to go.
| A．to tell | B．telling | C．having told | D．to telling |
. ______ hard. You are sure to succeed!
| A．Working | B．Work | C．Worked | D．To work |
There was a time _____ hunger was a disturbing problem in this area.
| A．how | B．when | C．that | D．why |